This invention relates generally to fuel burner systems and, more particularly, to solid fuel burner systems.
Many industrial processes require the equal distribution of heterogeneous flows to multiple receptors. For example in the electric utility industry, pulverized coal (“PC”) is transported through a pipe (duct) system that connects a grinding mill to one, or more, burners of a furnace. The PC is transported within the pipe system by a carrier gas, e.g., air. Thus, the heterogeneous flow, or stream, is made up of the PC and air (i.e., a two-phase flow or multi-phase flow). Ideally, one grinding mill is capable of supplying one or more such streams to multiple burners (receptors) of the furnace.
Unfortunately, as a stream moves through a long length of pipe, the solid particles in the stream tend to concentrate together in a pattern generally characterized as being in the shape of a rope strand. This phenomenon is commonly referred to as roping, or laning. As such, any attempt to further distribute, or split, a stream into multiple streams for transport to respective receptors seldom, if ever, yields equal amounts of PC going to each of the receptors. In other words, when roping occurs in a stream, splitting that stream into multiple streams results in a flow imbalance between the multiple streams. This flow imbalance could be on the order of ±30% between the multiple streams.
Likewise, with respect to receptors fed by multiple sources, roping makes it difficult to combine the flows from these multiple sources such that each of the receptors are supplied with equal flows.
The prior art has attempted to resolve these problems in several ways. For example, the installation of adjustable orifices to each carrier pipe and adjusting the resistance through each orifice is one method to reduce the range of imbalances in the flow. This method, although helpful, does not provide predictable results in all cases.
More recently, on-line flow measurement devices have been developed that can provide real-time information on the relative coal and air flows in each pipe. The use of this monitoring equipment, in combination with the above-mentioned adjustable orifices, permits the measurement and modification of the flows. However, a significant limitation of this method is the requirement for continuous adjustments using complex computer-controlled algorithms.
As such, these and other methods are generally ineffective, both in cost, effort, and time, to rectify flow imbalance. Indeed, many methods suffer from the general inability to attain satisfactory flow balance and maintain flow balance over time; the inability to prevent high-pressure drop requiring excessive power consumption; and the inability to prevent nonlinear flow balance as flow quantity changes.